From the Apple menu, choose System Preferences to open the System Preferences window.

Click the Desktop & Screen Saver button.

Click the Desktop tab; the left pane lists the different folders from which you can choose an image. The right pane displays thumbnails, small images, of the images in the selected folder.

Click Apple Images to select it. You'll see the default picture in the right pane, along with a bunch of other images.

Click any thumbnail to instantly change the desktop image. Feel free to click a few different ones to try them out.

Now select Nature in the left pane. Then click any of its thumbnails to place a nature type picture on your desktop. Do the same for Abstract.

If you'd rather have a solid color desktop, select Solid Colors in the left pane, and select a color swatch from the right pane.

When satisfied with your choice, close the Preferences window.

Of course, you can turn any of your own photos or artwork into a desktop picture too. Here's how to do this:

From the Apple menu, choose System Preferences.

In the window, click Desktop & Screen Saver, then click the Desktop tab to display just the desktop preferences.

If you want to use a photo from your iPhoto Library, select Library in the left pane. Otherwise, select Choose Folder, navigate to and select the folder that contains your image, and click Choose.

In the right pane, click any thumbnail to place the image on the desktop.

Depending on the size of your chosen image, you can opt to tile or center it if it's small. Note: Your image will look pixelated or have jagged edges if it's too small. Or have the image fill the screen, or stretch to fill the screen. Just choose an item from the pop-up menu that appears above the thumbnails, the one next to the thumbnail of your current picture.

If an image is too small to display satisfactorily as a full screen image,
you can choose Tile from the pop-up menu.

You can also have your Mac automatically change your desktop picture. To do this:

Select the "Change picture" checkbox. Note: This option is not available if you selected your iPhoto Library or an iPhoto picture roll.

From the Change picture pop-up menu, choose one of the intervals listed in the menu (such as every minute or every day—or choose every 5 seconds for a desktop slideshow).

Select the "Random order" checkbox if you want the images to appear at random. If it isn't selected, your images will appear in alphabetical order by name.